1. Field of the Invention
The present invention relates to a semiconductor device, a manufacturing method thereof and a method of forming a resist pattern used therein. More particularly, the present invention relates to a semiconductor device having a conducting material film formed in a trench, a manufacturing method thereof and a method of forming a resist pattern used therein.
2. Description of the Background Art
In the field of a DRAM (Dynamic Random Access Memory), which is conventionally known as one type of the semiconductor device, efforts have been made to increase capacity and miniaturize the device. Along with these efforts and achievements, to secure a capacity necessary for a capacitor cell, which is an element of a DRAM, within a limited area of a semiconductor substrate, three-dimensional cells such as a trench type cell or a stacked type cell have been developed. Among the stacked capacitor cells, those with vertically long shape such as a cylindrical type cell or a thick film type cell are mainly used.
FIGS. 17-19 show partial sectional views of a cylindrical stacked capacitor cell, on which the present invention is based and which is referenced for describing the manufacturing process of a lower electrode of a capacitor. With reference to FIGS. 17-19, the manufacturing process of the capacitor lower electrode of the cylindrical stacked capacitor cell will be described.
As shown in FIG. 17, a first interlayer insulation film 115 is formed on a semiconductor substrate (not shown). Openings 116a and 116b are formed in first interlayer insulation film 115. Plugs 117a and 117b are formed respectively in openings 116a and 116b for electrically connecting the capacitor lower electrode and a conducting region in a main surface of the semiconductor substrate. A second interlayer insulation film 123 is formed on first interlayer insulation film 115. Trenches 130a and 130b are formed in second interlayer insulation film 123 in regions above plugs 117a and 117b. Polycrystalline silicon film 119 is formed on second interlayer insulation film 123 as well as in trenches 130a and 130b. An HSG (Hemi Spherical Grained) polycrystalline silicon film 120 having a resist 127 formed thereon is formed on polycrystalline silicon film 119. Here, HSG polysilicon film means a polysilicon film having roughened surface, and to roughen (roughening) refers to a process of generating hemispherical grains by growing crystal grains.
With etch back of resist 127 using Reactive Ion Etching (hereinafter referred to as RIE), portions 127a and 127b of resist are left in trenches 130a and 130b as shown in FIG. 18 while resist 127 (see FIG. 17) is removed in other regions. Here, the level difference L1 between an upper surface of HSG polycrystalline silicon film 120 on second interlayer insulation film 123 and an upper surfaces of resists 127a and 127b is called recess length. As will be described hereinafter, as portions 127a and 127b of resist are used as masks for removing polycrystalline silicon film 119 and HSG polycrystalline silicon film 120 on second interlayer insulation film 123, the recess length L1 must be controlled with a high precision. If the recess length L1 is too small and the upper surfaces of resist portions 127a and 127b are higher than the upper surface of second interlayer insulation film 123, problems arise. For example, upon etching for removing polycrystalline silicon film 119 and HSG polycrystalline silicon film 120 on the upper surface of second interlayer insulation film 123, etching residue may be produced.
Then using resist portions 127a and 127b as masks, polycrystalline silicon film 119 and HSG polycrystalline silicon film 120 on the upper surface of second interlayer insulation film 123 are etched and removed. Thus a capacitor lower electrode of polycrystalline silicon film 119a and HSG polycrystalline silicon film 120a is formed in trench 130a and a capacitor lower electrode of polycrystalline silicon film 119b and HSG polycrystalline silicon film 120b is formed in trench 130b as shown in FIG. 19.
Then resist portions 127a and 127b are removed and a dielectric film, a capacitor upper electrode and so on are formed on the capacitor lower electrode. The cylindrical stacked capacitor cell is thus formed.
The process shown in FIGS. 17-19 has a following problem. When the resist is etched back by RIE to leave resist portions 127a and 127b only in trenches 130a and 130b as shown in FIG. 18, an oxide film or the like is sometimes partially formed on the surface of HSG polycrystalline silicon film 120 on the upper surface of second interlayer insulation film 123. The oxide film thus formed through RIE serves as a mask upon etching of polycrystalline silicon film 119 and HSG polycrystalline silicon film 120 for isolating the capacitor lower electrode trench by trench. Therefore polycrystalline silicon film 119 of HSG polycrystalline silicon film 120 is sometimes partially left on the upper surface of second interlayer insulation film 123.
When polycrystalline silicon film 119 or the like is left on the upper surface of second interlayer insulation film 123, the capacitor lower electrode is not sufficiently isolated, and whereby a problem such as short circuit of the capacitor lower electrode is caused. As a result, operation failure and reliability degradation of the DRAM occur.
Alternatively, CMP (Chemical Mechanical Polishing) can be used for removing resist 127 (see FIG. 17) in the region outside trenches 130a and 130b for leaving resist portions 127a and 127b in trenches 130a and 130b. In this case, however, slurry used in CMP is left in the area such as an inner area of trenches 130a and 130b, and adversely affects the subsequent process steps. The slurry thus left in trenches 130a and 130b also causes operation failure and reliability degradation of the semiconductor device such as a DRAM.
An object of the present invention is to provide a highly reliable semiconductor device having a conducting material film formed in a trench.
Another object of the present invention is to provide a method of manufacturing a highly reliable semiconductor device having a conducting material film formed in a trench.
Still another object of the present invention is to provide a method of forming a resist pattern which can be used in the method of manufacturing the highly reliable semiconductor device having the conducting material film formed in the trench.
In the method of manufacturing the semiconductor device according to one aspect of the present invention, an underlying film having an upper surface and a trench is formed. A conducting material film is formed on the upper surface and in the trench. A photo resist film is formed on the conducting material film which is located on the upper surface of the underlying film and in the trench. The photo resist film is left in the trench whereas in other region the photo resist film is developed and removed. With the photo resist film left in the trench used as a mask, the conducting material film on the upper surface of the underlying film is etched and removed.
Thus, an etching technique such as RIE which is used in a conventional manufacturing process is not employed in the step of leaving the photo resist film in the trench and removing the photo resist film in the region outside the trench. Therefore the formation of oxide film on the conducting material film caused by etching can be prevented. As a result, in the step of removing the conducting material film on the upper surface of the underlying film, the conducting material film is prevented from being partially left on the upper surface of the underlying film because of the existence of the oxide film. Thus, failure such as short circuit caused by the residual conducting material film can be avoided, whereby a highly reliable semiconductor device can be obtained.
In addition, as the development is utilized in the step of leaving the photo resist film in the trench, the thickness of the photo resist film to be removed and therefore the level of the upper surface of the photo resist film left in the trench can be controlled with high precision by controlling the time of development.
In the method of manufacturing the semiconductor device in accordance with one aspect of the present invention, the photo resist film in the region outside the trench may be exposed before the development.
Then the thickness of the exposed photo resist film, which is to be removed in the step of removing the photoresist film outside the trench, can be controlled by the control of exposure energy when a positive photo resist film is used. Therefore, the level of the upper surface of the photo resist film left in the trench can be controlled more surely.
In the method of manufacturing the semiconductor device in accordance with one aspect of the present invention, the photo resist film in the region outside the trench may be completely exposed whereas the photo resist film to be left in the trench may not be exposed in the step of exposing the photo resist film.
As the photo resist film in the trench is not exposed when the positive photo resist film is used, the photo resist film can surely be left in the trench after the development.
In the method of manufacturing the semiconductor device in accordance with one aspect of the present invention, light used for the exposure may be directed obliquely for irradiation to the upper surface of the underlying film in the step of exposing the photo resist film.
Thus the light is prevented from reaching the bottom portion of the trench, because the light for exposure is not in a direction perpendicular to the extension of the upper surface of the underlying film. Therefore the exposure of the photo resist film at the bottom portion of the trench can surely be prevented. As a result, the photo resist film can surely be left in the trench.
In the method of manufacturing the semiconductor device in accordance with one aspect of the present invention, an angle of incidence of the light used for exposure with respect to the upper surface of the underlying film may be adjusted so that the light does not reach the photo resist film to be left in the trench in the step of exposing the photo resist film.
Thus the exposure of the photo resist film to be left in the trench can even more surely be prevented and the photo resist film can surely be left in the trench. In addition, the location in the trench where the light reaches can be adjusted by adjusting the angle of incidence of the light used for exposure with respect to the upper surface of the underlying film. As a result, the level of the upper surface of the photo resist film left in the trench can be controlled with high precision.
In the method of manufacturing the semiconductor device in accordance with one aspect of the present invention, the step of forming the underlying film may include the steps of: forming an underlying film with a planar upper surface; forming a resist pattern for forming a trench on the upper surface using a photo resist film for pattern formation; and forming the trench by removing the underlying film using the resist pattern as a mask. The photo resist film may be less sensitive to the light than the photo resist film for pattern formation.
Thus, even when the exposure energy upon photo resist film exposure varies, the fluctuation of the thickness of the exposed portion of the photo resist film can be made smaller than when the photo resist film for pattern formation is used. As a result, the fluctuation of the level of the upper surface of the photo resist film left in the trench can be made smaller than in a conventional art.
In the method of manufacturing the semiconductor device in accordance with one aspect of the present invention, the step of forming the photo resist film may include a step of forming the photo resist film such that the non-exposed portion with the thickness of the photo resist film to be left in the trench is left even when the exposure energy is increased in the step of exposing the photo resist film.
Thus the delicate control of the exposure energy in the step of exposing the photo resist film is not necessary for adjusting the thickness of the exposed portion of the photo resist film and for leaving the non-exposed portion of the photo resist film with the necessary thickness in the trench. Therefore, even when the exposure energy varies, and even if the light with the exposure energy above a predetermined value is directed to the photo resist film, the non-exposed portion with a predetermined thickness can be formed and whereby the photo resist film with the predetermined thickness can surely be left in the trench.
In addition, as the thickness of the exposed portion can be determined by the chemical composition of the photo resist film, the thickness of the non-exposed portion of the photo resist film can be controlled with higher precision than when the thickness of the exposed portion is controlled by adjusting the exposure energy. As a result, more precise control of the level of the upper surface of the photo resist film left in the trench is allowed.
The method of manufacturing the semiconductor device in accordance with one aspect of the present invention may further include the step of forming under the photo resist film, a light absorption film absorbing the light used in the step of exposing the photo resist film.
Thus the light is prevented from reaching inside the underlying film, because of the existence of the light absorption film. Therefore, the exposure of the side surface and so on of the photo resist film in the trench, caused by the entrance and scattering of the light used in the step of exposing the photo resist film, in the underlying film under the photo resist film, can be prevented. As a result, the photo resist film can surely be left in the trench.
In the method of manufacturing the semiconductor device in accordance with another aspect of the present invention, an underlying film having an upper surface and a trench is formed. A conducting material film is formed on the upper surface and in the trench. A photo resist film having an upper surface is formed on the conducting material film in the trench. The level of the upper surface of the photo resist film is made lower than the level of the upper surface of the underlying film through curing of the photo resist film. The conducting material film on the upper surface of the underlying film is etched and removed with the use of cured photo resist film as a mask.
Here, the curing is a treatment for hardening and shrinking the photo resist film by directing an ultra violet ray (Deep UV) or conducting a heat treatment on the photo resist film. At curing time longer than a predetermined period, volumetric shrinkage of the photo resist film shows a certain threshold value.
Because of this certain threshold value of volumetric shrinkage of the photo resist film at the curing time longer than a predetermined amount, with the adjustment of the thickness of the photo resist film prior to the curing, the height of the upper surface of the photo resist film after the curing can be correctly controlled.
In addition, the formation of the oxide film on the conducting material film can be prevented because technique such as RIE is not employed in the step of forming the upper surface of the photo resist film at a level lower than the upper surface of the underlying film. Thus in the step of removing the conducting material film located on the upper surface of the underlying film, a portion of the conducting material film is prevented from being left on the upper surface of the underlying film, which is caused by the existence of the oxide film. As a result, failure such as a short circuit which is attributable to the residual conducting material film can be prevented, and whereby a highly reliable semiconductor device can be obtained.
In a method of forming a resist pattern in accordance with still another aspect of the present invention, the resist pattern is formed on an underlying film having an upper surface and a lower upper surface lower than the upper surface and adjacent to the upper surface with a step side wall therebetween. In this method, a photo resist film is formed on the upper surface, the step side wall, and the lower upper surface. The photo resist film formed in a region other than the bottom portion of the step side wall is exposed by the light incident obliquely on the upper surface. A non-exposed portion of the photo resist film is left at the bottom portion of the step side wall and the exposed portion of the photo resist film is removed by development.
With the use of the light directed obliquely to the upper surface for the exposure of the photo resist film, the exposure of the photo resist film at the bottom portion of the step side wall can surely be prevented. Thus, the non-exposed portion of the photo resist film can surely be left at the bottom portion of the step side wall.
In addition, the amount of the photo resist film left at the bottom portion of the step side wall can be controlled through the adjustment of the angle of incidence of the light used for exposure with respect to the upper surface.
A semiconductor device in accordance with still another aspect of the present invention includes an underlying film having a trench, a conducting material film formed in the trench, and, a light absorption film formed on the conducting material film, for absorbing the light used in photolithography for forming the conducting material film.
Thus, in the step of forming the conducting material film in the trench, as the light used in the exposure/development is absorbed by the light absorption film, even when the photo resist film is formed in the trench and on the underlying film outside the trench, and the photo resist film outside the trench is removed by the exposure/development, the light is prevented from reaching the underlying film and the conducting material film. Therefore, the light is not scattered in the underlying film and the conducting material film, and the exposure of the side surface and the bottom surface of the photo resist film in the trench can be prevented. As a result, the photo resist film can surely be left in the trench. Thus the failure caused by the partial absence of the photo resist film in the trench, such as the removal of the conducting material film which is to be left in the trench can be prevented in the step of forming the conducting material film in the trench.
In the semiconductor device in accordance with the still another aspect of the present invention, the conducting material film may be a capacitor lower electrode, and the device may further include a dielectric film formed on the capacitor lower electrode and a capacitor upper electrode formed on the dielectric film.
In the semiconductor device in accordance with the still another aspect of the present invention, the light absorption film may be a silicon nitrided oxide film.
The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.